The purpose of this K01 Mentored Research Scientist Development Award application is to facilitate my training in the field of sleep and pediatric bipolar disorder (PBD) and in so doing, support my short-term objectives to: (1) comprehensively characterize sleep and circadian rhythms in adolescents with bipolar disorder (BD), and (2) investigate the relationship between sleep/circadian dysregulation and mood dysregulation in this population. The proposed training and research project represent the key first step in laying the groundwork for a long-term independent, academic, clinical research career focused on sleep and circadian dysregulation in the onset, development, course, and treatment of pediatric mood disorders. Multiple lines of evidence suggest that sleep/circadian disruptions are core features of adult BD, and that these disruptions may trigger episodes of illness. However, there is virtually no information on the nature and severity of sleep/circadian disruption in PBD, or on the potential contribution of sleep/circadian disruption to mood dysregulation. Given incidence rates of BD peak during adolescence and that BD is associated with particularly devastating outcomes when onset is early in life, adolescence offers a critical window for understanding the development of this disorder. Previous studies assessing sleep and circadian functioning in PBD samples have largely relied on subjective measures. The proposed research study will be the first to use a comprehensive, ecologically sensitive, and objective characterization of sleep/circadian rhythms in adolescents with BD relative to controls. This assessment combines two nights of ambulatory polysomnography (PSG), along with a two- week observation period of continuous actigraphy, and daily monitoring of subjective sleep, social rhythms, and affect. Daily measures of social interaction, stress, and rumination will also be collected. By investigating sleep in bipolar youth, the proposed study aims to address a gap in knowledge on the role of sleep and circadian disruption in the early development and progression of PBD. The hypotheses predict group differences in: (H1a) sleep architecture, specifically sleep efficiency, REM latency, and REM density and duration; (H1b) sleep and wake durations, sleep fragmentation, and daytime activity level; (H1c) overall rates of sleep disorders; (H1d) subjective sleep measures and regularity of social rhythms. The proposed investigation will also examine a potential link between daily sleep and daily affect in order to test for group differences in (H2) the degree of sleep-affect coupling. The proposed integrated program of research, mentorship and didactic training, combined with the outstanding research environment at Stanford University will foster my long-term career objective to be an independent investigator of sleep and circadian mechanisms in pediatric mood disorders.